On 2019/1/7 上午11:28, Michael S. Tsirkin wrote:

On Mon, Jan 07, 2019 at 10:19:03AM +0800, Jason Wang wrote:

quoted

On 2019/1/3 上午4:47, Michael S. Tsirkin wrote:

quoted

On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:

quoted

This series tries to access virtqueue metadata through kernel virtual
address instead of copy_user() friends since they had too much
overheads like checks, spec barriers or even hardware feature
toggling.

Will review, thanks!
One questions that comes to mind is whether it's all about bypassing
stac/clac.  Could you please include a performance comparison with
nosmap?

On machine without SMAP (Sandy Bridge):

Before: 4.8Mpps

After: 5.2Mpps

OK so would you say it's really unsafe versus safe accesses?
Or would you say it's just a better written code?

It's the effect of removing speculation barrier.

quoted

On machine with SMAP (Broadwell):

Before: 5.0Mpps

After: 6.1Mpps

No smap: 7.5Mpps


Thanks

no smap being before or after?

Let me clarify:


Before (SMAP on): 5.0Mpps

Before (SMAP off): 7.5Mpps

After (SMAP on): 6.1Mpps


Thanks

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